Fire Rated Floor Assemblies for Steel Framed Construction

October 16, 2018

Ref: Fire Rated Floor Assemblies – Oct 2018 – Cold-formed steel framing continues to go from strength-to-strength as a sustainable, durable and cost-effective way to construct mid-rise buildings (although a recent feasibility study from the SFIA suggests that cold-formed steel could in fact be a viable framing option for buildings of 40 storeys or more).

Given the strong focus in this sector on multi-story residential, dormitories, hotels, schools, hospitals, assisted living facilities, correctional facilities and the like, it is no surprise that steel’s non-combustibility is a significant factor in this popularity.

As a non-combustible material, steel will not contribute in its own right to the spread of fire, reducing the fire risk to occupants, firefighters and property/business owners.

But of course the correct choice of materials, design and implementation of fire rated floor assemblies in steel framed buildings is equally critical.

Non-Combustible Subfloor Materials: Plycem SX20/20™

USAP’s Plycem SX20/20™ is a non-combustible building material designed specifically for the construction of fire rated floor assemblies in steel framed buildings (as well as being suitable for wood joists and hot-rolled steel framing, typically for retrofit or renovation projects).

As well as meeting the criteria of ASTM E136 as a non-combustible building material, it also achieves zero flame spread and zero smoke development in its ASTM E84 test results.

This span-rated fiber cement subfloor panel is strong, durable and dimensionally stable. The boards (available in 3/4” and 1” thicknesses) are factory sealed against water absorption – so they won’t buckle or warp like wood sheathing. However the boards do actually install like wood sheathing, requiring only a circular saw for cutting and screws for fastening.

All of this, combined with outstanding cost-effectiveness, make Plycem SX20/20™ the natural choice for the construction of fire rated floor assemblies in cold-formed steel frame buildings.

Fire Rated Floor Assemblies: Plycem SX20/20™

The fire rated floor assembly is typically formed by mechanically fastening Plycem SX20/20™ panels to cold-formed steel joists, trusses or framing members. The Plycem SX20/20™ floor is then finished with a traditional finishing floor cover such as ceramic tile, vinyl, wood or carpet.

The void is insulated, and a non-combustible ceiling assembly is then attached to the bottom of the floor joists to complete the construction.

UL H504, shown below (full assembly test results are available for download on our SX20/20™ page), is a typical 1 hour fire rated floor assembly. Here, a 3/4” Plycem SX20/20™ tongue-and-groove decking is mechanically fastened to the joists; mineral wool batts are laid in the concealed void; and a single layer of 5/8” Type C gypsum board secured to complete the ceiling assembly.

In more general terms, the specific fire rating for a Plycem SX20/20™ fire rated floor assembly will depend on a number of factors, including: the material and construction of the ceiling assembly (including whether a single or double layer); the depth of the concealed void; the insulation materials used; and a range of specific assembly details such as the placement of batts over furring channels.

Inevitably, the full range of these variables is impossible to cover in an article of this nature. Instead, the USAP team provides a custom technical service designed to help customers find exactly the right boards, assemblies and solutions for each individual project. Please do contact us today to discuss the right product and assembly choices your project.

Fire Rated Floor Assemblies: Versaroc

In certain circumstances, USAP’s Versaroc panels may be the most appropriate choice for your fire-rated floor assembly.

Versaroc, a cement-bonded particle board (CBPB) with Portland cement and mineralized fibers at its heart, is another great value structural panel, but one with slightly different properties to SX20/20™.

Like SX20/20™ it is environmentally safe, strong and highly fire resistant, with zero flame spread and smoke development in ASTM E84 testing, and 1 & 2 hour fire rated floor assemblies available per ASTM E119.

But Versaroc’s slightly different composition contributes to a number of additional and useful properties, such as

Anti-fungal properties and moisture resistance make it ideal for cold storage, food processing and similar areas where hygiene is paramount.

It is worth noting in fact that Versaroc’s unique properties mean that as well as fire rated floor assemblies, this high-performance CBPB panel is ideally suited to roofing, access flooring, sound barriers, exterior and interior wall construction and structural insulated panels (SIP). As such, Versaroc is found in use across the world in buildings as diverse as schools, assisted living facilities, multi-story residential, hospitals, factories, universities, dormitories, correctional facilities, airports, hotels and much more.

Fire Rated Floor Assemblies: Your Project

While this article has sought to cover a number of the key issues involved in fire rated floor construction, each project is of course unique.

For that reason, as well as providing market-leading cement board products, USAP remains committed to helping its customers find exactly the right products, assemblies and solutions for each and every project.

Our approach is consultative throughout, meaning we will respond rapidly to requests for technical information, special orders, customization or other unique project requirements. Please do contact the USAP team today to discuss your project.